A Technique for Measuring ELF Magnetic Shielding Effectiveness

Summary form only given. As the concentration of equipment or the power requirements increase, magnetic fields having power source fundamental and harmonic frequencies increase. The use of Silicon Controlled Rectifiers for speed and power control of machine tools cause additional magnetic fields at harmonic frequencies of the fundamental power source frequency. Shielding of sensitive circuits and equipment becomes increasingly important. This paper describes the techniques used to evaluate magnetic shielding effectiveness of shielded enclosures in the frequency range of 10 cps to 5 Kc. This frequency range can easily be extended above 15 Kc. It involves the use of a wideband variable-mu receiver as the magnetic field sensing instrument. This technique would be applicable to evaluation of various materials, construction techniques, and configurations of shielded enclosures for magnetic shielding effectiveness.